A decision support system for power plant design

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<ul><li><p>A decision support system for power plant design</p><p>Fatima C.C. Dargam *, Erhard W. Perz</p><p>SimTech Simulation Technology, Riesstrasse 120, A-8010 Graz, Austria</p><p>Received 1 March 1997</p><p>Abstract</p><p>The design of power plants requires a balanced study of three major considerations, namely: the decision about the</p><p>plant lay-out (choice of components and their dispositions); the planning of the plant operational requirements (pro-</p><p>vision for maintenance and upratings); and the variation of external conditions, like changes on energy costs or on the</p><p>demand rates, for instance. These three aspects must be jointly dealt with, considering both quantitative and qualitative</p><p>classifications which cover economic and technical requirements of the project design. The available tools for design</p><p>and simulation of power plants, provide support for technical quantitative analysis. However, they do not support</p><p>the design qualitatively. In this paper, we propose to incorporate a decision support system in a power plant simulation</p><p>tool, in order to provide the qualitative synthesis needed for the plant design process, and also to assist the design en-</p><p>gineers in performing a better choice-evaluation of the aspects described previously. The paper describes the systems</p><p>specification and initial implementation details within the simulation framework of IPSEpro, a programmable integrat-</p><p>ed process simulation environment from SimTech. 1998 Elsevier Science B.V. All rights reserved.</p><p>Keywords: Decision support systems; Power plant design; Process simulation; Qualitative analysis; Evaluation support;</p><p>Knowledge-based support systems</p><p>1. Introduction</p><p>The ability to model power plant equipmentand complete power plants is essential for optimiz-ing the performance and consequently cuttingdown costs. For many years, computer modelshave been important tools for this area. In the be-ginning, the tendency was for companies to havelarge proprietary programs, implementing their</p><p>specific design concepts and know-how. The rapiddevelopment of computing technology during re-cent years made maintenance of such programsdicult and costly. Nowadays, most of the compa-nies including equipment manufacturers, plant op-erators, and engineering and consultingcompanies, prefer to use modelling environmentsthat allow them to overcome the limits of purposespecific solutions. As a consequence, projects per-formance was improved and productivity increas-ing features, like graphic user interfaces andecient data exchange with other programs, weremade available to them. An example of a software</p><p>European Journal of Operational Research 109 (1998) 310320</p><p>* Corresponding author. Fax: 43 316 386 278/9; e-mail:</p><p>f.dargam@simtechnology.com.</p><p>0377-2217/98/$19.00 1998 Elsevier Science B.V. All rights reserved.PII S 0 3 7 7 - 2 2 1 7 ( 9 8 ) 0 0 0 5 9 - 9</p></li><li><p>system with these capabilities is SimTechs pack-age IPSEpro.</p><p>Designing power plants is a highly domain de-pendent task. It requires a balanced study of threemajor considerations, namely: the decision aboutthe plant lay-out (choice of components and theirdispositions); the planning of the plant operationalrequirements (provision for maintenance and up-ratings); and the variation of external conditions,like changes on energy costs or on the demandrates, for instance. In [1], we find these aspects de-scribed in detail. These three aspects must be joint-ly dealt with, considering both quantitative andqualitative classifications which cover economicand technical requirements of the design project.The available tools for design and simulation ofpower plants, provide support for technical quan-titative analysis, but they do not support the de-sign qualitatively. There is a need for theintegration of a design support module into a pow-er plant simulation environment, so that users canbe assisted in performing a better choice-evalua-tion of the aspects described previously. Such asupport system would also provide the qualitativesynthesis needed for the plant design process.</p><p>This paper describes the integration of a DesignSupport System to the programmable integratedprocess simulation environment IPSEpro.</p><p>2. Related work</p><p>In the area of power plant design support, wefind studies of methodic approaches, like the onepresented in [1], which helps to specify optimizedlay-outs and operation strategies of thermal powerplants. Within such a methodological approach topower plant design, we identify three phases wherea decision support system could be usefully ap-plied: Providing feasible solutions considering triple</p><p>variations of plant-design parameters, plantoperation parameters, and existing boundaryconditions.</p><p> Providing basis for the implementation of inno-vative solutions, by identifying knowledgegaps which are required to deal with criticalparts of the project.</p><p> Supporting the plant modelling, in terms ofcomponents choice and qualitative synthesis inorder to meet the expected output parameters,considering the existing boundary conditions.By boundary conditions we mean, for in-</p><p>stance, parameters involving physical, economic,and legal constraints.</p><p>In the area of power plant operation support,we know of prototype implementations in termsof decision support systems. As an example we citethe work in [2], where they describe the develop-ment of a knowledge-based operator support sys-tem for small cogeneration plants. The objectiveof their system is to support operators, who maybe either present at the plant or remote operators,in deciding if the plant operates according to ex-pectancy. Results are achieved by comparing themeasured plant state to a model of normal opera-tion, stored in the systems knowledge base. Theknowledge consists of a combination of thermody-namic relationships achieved from the plant designphase, and rules derived from the operators work-ing experience.</p><p>Ideally, one can think of a unifying frameworkembedding both design and operation support sys-tems for power plant modelling and control. Sucha framework would be able to combine the result-ing features of both systems as feedback, in orderto gain considerably in the whole project designand operation. As a consequence, the overall sys-tem would provide the operator with the design in-formation about the optimized operation of theplant. In return, it would get feedback informationfrom the operators to the design engineers, aboutthe theoretic data checked against the real behav-iour of the plant.</p><p>The development of a modelling frameworkunifying both design and operation support sys-tems, as the one mentioned above, is our ultimategoal. In this paper, however, we limit ourselves indescribing the development of a decision supportsystem for power plant design only.</p><p>3. Power plant design support</p><p>The idea of a decision support system, as it wasfirst formulated in [3], is to support rather than</p><p>F.C.C. Dargam, E.W. Perz / European Journal of Operational Research 000 (1998) 000000 311</p></li><li><p>replace decision makers, to solve semi and unstruc-tured problems. The lack of structure can reside invarious aspects of a decision problem. For in-stance, data about the initial state of the problemcan be unavailable; the goals to be achieved canbe unclear; constraints can be unknown; and/ordecision consequences can be poorly predictable.Furthermore, the meaning of problem can varyfrom a vague to a very exactly specified concept.We consider here the definition stated in [4]:</p><p>\By a problem we mean a situation that satisfiesthree conditions: First, a decision-making individualor group has alternative courses of action available;second, the choice made can have a significant eect;and third, the decision maker has some doubt as towhich alternative should be selected".</p><p>The primary goal of integrating a decision sup-port system into power plant modelling, is to pro-vide computational basis for the implementationof innovative solutions, enforcing the optimizationof such projects.</p><p>As pointed out in [1], the main reasons for op-timizing energy systems design rely on the follow-ing facts: Adoption of new solutions, leading to successful</p><p>innovations, are sometimes hard to be imple-mented due to lack of confidence and knowledgeto abandon non-ecient existing solutions. Thisimplies that appropriate structuring methods inthe modelling of energy systems have been insuf-ficient to provide technical innovations. An ex-ample of such successful innovation, in thearea of thermal power plant design, was the es-tablishment of the combined-cycle technology.</p><p> The number of failure analysis, specially of ther-mal power plants, has considerably increasedover the recent years. This implies that impor-tant operation conditions and technical varia-tions, have not suciently been taken care of.The available computational tools for the de-</p><p>sign and simulation of energy systems, providesupport for engineering technical systems which,most of the times, are conceived disregarding realand feasible solutions.</p><p>Within this context, we define the support to beprovided in the power plant design system pro-posed here, in two levels: the plant modelling level,and the innovative solutions level.</p><p>Plant modelling support: The plant modellingsupport involves decisions on the choice of theplant type to be modeled, and on the choice ofthe components to be used by the plant. This sup-port level also caters for the projects qualitativesynthesis in order to meet the expected output pa-rameters, like physical, economical and legal con-straints. Inferences are performed by the designsupport system along dierent phases of this sup-port level. The inference process prompts the de-sign engineer with the possible and/or requiredchoices for a project decision.</p><p>Innovative solutions support: This support levelprovides the basis for the implementation of inno-vative solutions, by identifying knowledge gapswhich are required to deal with critical parts ofthe project. In this level, the design support systemis supposed to identify the projects critical parts;explain their critical nature; and suggest technicalmodifications according to its database of innova-tive solutions examples.</p><p>The implementation of the proposed designsupport system is specified to interface with IPSE-pro, SimTechs modelling package for energy sys-tems. IPSEpro is used to create the structuralmodel (process scheme) of the plant, as well as toprovide its simulation analysis. It includes compo-nent model libraries to attend a wide range of pow-er plants.</p><p>4. The IPSEpro-DSS module</p><p>We introduce this section by presenting somebackground information about IPSEpro and itsmodules.</p><p>4.1. The environment IPSEpro</p><p>IPSEpro is a flexible environment that providesfacilities for creating models of components, forsetting up models of equipment or of a completepower process, and for solving these models. Thedesign structure of the system IPSEpro allowsusers to calculate any process that can be repre-sented by a network of discrete components andtheir connections. Process models can be created</p><p>312 F.C.C. Dargam, E.W. Perz / European Journal of Operational Research 109 (1998) 310320</p></li><li><p>by appropriately connecting component modelsfrom a library, which can be a standard or any spe-cific library of components.</p><p>The component level flexibility: IPSEpro pro-vides high flexibility in defining the characteristicsof the component models that are used for model-ling complete processes. This allows users to buildcomponent model libraries that exactly matchtheir application requirements. The models are de-signed both mathematically and graphically, with-in IPSEpros Model Development Kit (MDK).Modification and customization of existing com-ponent models from standard model libraries arealso possible. MDK provides a model descriptionlanguage (MDL) that allows users to describe theirmodels mathematically, once their equations areidentified. MDKs interface contains an icon edi-tor that further facilitates the development of thecomponent models graphically. MDKs modelcompiler translates the model descriptions into aformat that is used when a process model is solved.</p><p>The process level flexibility: IPSEpro gives userstotal freedom in arranging the available compo-nents in order to represent a process scheme. Agraphical user interface facilitates the developmentof process schemes, and the presentation of the re-sults of calculations. To set up a process model,the design engineer chooses component icons froma library menu, places and connects them appro-priately in the project window of IPSEpros Pro-cess Simulation Environment (PSE). Numericaldata and results of process calculations are enteredand displayed directly in the project window. PSEgenerates output protocols automatically, in theend of the simulation process.</p><p>IPSEpro is based on the concept of standard-ized components that are used to build the modelof a complete process. Each model is mathemati-cally represented by a set of equations and vari-ables. To build the mathematical model of aprocess means to join all equations of the compo-nent models into a single system of equations. Tosolve a system of equations, PSE adopts a 2-phaseapproach:1. Analysis In this phase PSE determines the op-</p><p>timum solution method. It analyses the order inwhich it can solve variables of a model, andcombines equations into groups for the sakeof gaining speed in the solution process.</p><p>2. Numerical solution In this phase PSE solvesthe equations in the order pre-established andwith the numerical methods pre-defined bythe analysis phase. More details about thesystems solution process can be found in[5,6].The structure of IPSEpro with its main modules</p><p>MDK and PSE, has the advantage of well-definingthe projects flow of data. In most cases, a modellibrary is used by many projects. Therefore, chan-ges in the model library may have far reachingconsequences, which makes the projects mainte-nance a much easier task. Frequently the authorof a model library is dierent from the actual userof the library. The user of the library will then onlyuse PSE, so that accidental changes of the libraryare not possible. Library changes can only bemade by qualified persons, who can also betterjudge their possible consequences in the projectsinvolved [7]. Fig. 1 illustrates the flow of datawithin the structure of IPSEpro.</p><p>Fig. 1. IPSEpro system structure.</p><p>F.C.C. Dargam, E.W. Perz / European Journal of Operational Research 000 (1998) 000000 313</p></li><li><p>The standard libraries currently available forIPSEpro are: the APP-Lib for power plant simula-tions; the gas-turbines library; and the heat-ex-changers library. The advanced power plantlibrary was designed for modelling a wide rangeof thermal systems. This library contains modelsfor both design and o-design analysis of anypower plant, including: combined-cycle plants; co-generation plants; and conventional plants. Thegas-turbines library was designed to be used inconjunction with the APP-Lib for the design ofpower plants. It contains models of the most usedgas turbines of several dierent manufacturers.Th...</p></li></ul>


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